1. Field of the Invention
The present invention relates to a soft-frozen desert apparatus designed specifically for self-service restaurants, eliminating the shortcomings of using traditional soft-serve self-contained frozen desert machines designed for an over-the-counter mode of operation.
2. Description of the Related Art
Conventionally, self-service restaurants and cafes use the soft-serve frozen dessert machines designed specifically for over the counter operations. Soft-serve machines are installed in the service room with their fronts facing the window-ports in the wall between the service and client areas. The fronts of the machines contain the dispensers and the control and monitor ring panels which are accessible to the clients through the window-ports. An example of such a machine may be found in U.S. Pat. No. 5,158,506 to Kusano et al.
Such restaurants are essentially divided into two spaces: client rooms and service rooms.
The machines for producing soft-serve frozen dessert, such as soft-serve ice cream and/or yogurt, may produce one or more flavors of the product. The most popular machines provide two flavors (e.g., vanilla and chocolate) and a mix of the original flavors. To produce each flavor the machine is equipped at least with a reservoir or a hopper for liquid mix, a cylindrical freezing barrel or a freezer and a low temperature refrigeration system. Most machines also have a medium temperature refrigeration system for keeping the liquid mix in the hopper at a safe temperature in the approximate range of 2° C. to 5° C. Liquid mix is either gravity-fed or pumped into the receiving chamber of the freezer. Air is injected into mix flow at a desired proportion. A geared motor rotates a shaft extending through the center of the freezer. A beater and a series of scrapers are mounted on the shaft. The beater mixes the liquid with air producing foam. The freezer is cooled by the coil, wounded-on the external surface of the freezer, to the temperature adequate to fast freeze a thin layer of foam touching the internal surface of the cylinder to the temperature considerably below the goal temperature of the product in the approximate range of −6.5° C.-−8° C. The rotating scrapers skim the frozen mix from the surface of the cylinder and fold it into the warmer mix in the center area of the freezer where it is mixed with warmer mix achieving optimal product temperature in the approximate range of −6.5° C.-−8° C. At the same time, the mix is propelled by the beater longitudinally through the freezing cylinder towards the dispensing head. The rotating beater also facilitates to build-up pressure in the dispensing chamber of the freezer that is adequate to create flow of the product when the dispensing valve is open.
Each machine, in most cases, has two hoppers and two freezers for producing two flavors of the product. Also machines may have a third dispenser for providing a mix of two original flavors. The machines are self-contained. They have all the refrigeration equipment to provide freezing the barrels of the freezers and cooling the mix in the hoppers to the safe temperatures (in the range of approximately 2° C. to 5° C.).
Such machines have multiple shortcomings when utilized in restaurants utilizing the self-service business model of operation.
The refrigeration capacity of each machine is selected to meet the requirement of cooling of the freezers and hoppers at the most demanding periods when the machines are started with warm mix in the hoppers and the freezers. Most of the time during normal operation, the cooling requirements are considerably lower to just freeze the new portion of the mix entered the freezer after the product is dispensed and compensate the heat gain from the environment. Those times require considerably lower freezing and cooling capacity. The machines balance the drop in refrigeration demand by cycling the compressors, in other words, employing the pulse width modulation or PWM technique. This technique, when applied to alternating current or AC motor driven compressors, is very energy inefficient. Moreover it sharply reduces the longevity of the compressors. Also the power demand of the whole installation is equal to the sum of the rated powers of all of the machines. In some cases this demand exceeds the available kW capacity of the desired location of the restaurant, limiting the business opportunity.
The air conditioning system, serving the installation must be sized with consideration of the total rated demand of all the machines, which may considerably increase the cost of the construction and in some cases makes the installation impossible.
Efficiency of any refrigeration system depends on “temperature lift”: the difference between the condensing temperature of the condenser and evaporating temperature of the evaporator. The lower the lift, the higher the efficiency. The condensing temperature equals the sum of the temperature of the cooling environment of the service area air temperature and the approach temperature. For example, if the kitchen temperature is approximately 25° C. and the approach temperature is approximately 15° C. then the condensing temperature is approximately 40° C. If the required temperature on an internal surface of the freezer barrel is approximately −20° C. and the freezer approach temperature is approximately 15° C. then the evaporation temperature is approximately −35° C. The temperature lift in this example is approximately 75° C.
To achieve the lower approach temperature it is necessary to increase the heat exchange surfaces which may be done by increasing the size or the condensing heat exchanger and the number of refrigeration coil rows (for air cooled exchanges) and velocity of the cooling media, which may be air or water. The existing self-contained soft service machines just do not have room to do that. In case of air cooled machines they usually have just one radiator with multiple condensing coils attached to it and a single fan.
The heat exchanges of the freezer cylinders prevailing in the industry are comprised of copper tubing with an internal diameter of approximately 5 mm winded and brazed on the external surface of the cylinder. Expanded refrigerant flows through the tubing and evaporates at temperatures in the range of approximately −35° C. to −20° C. The evaporating temperature depends on the total heat transfer coefficient between the refrigerant and the layer of the mix contacting the inside wall of the cylinder. A major component of the total heat transfer resistance depends on the efficiency of heat transfer between the refrigerant and the internal surface of the copper tubing. When the refrigerant enters the heat exchanger its quality is in the range of approximately 25% to 35%. At these conditions the refrigerant comprises small droplets of liquid suspended in saturated gas. Gas has a very low heat transfer coefficient so the heat transfer from the internal surface of the tubing to the droplets inside is greatly inhibited. Primarily the heat transfer occurs between a thin layer of refrigerant condensed on the internal surface of the tubing and the tubing. So the intensity of heat exchange increases when the ratio of the internal perimeter of the cross-section of the tubing to its area drops. So using the traditional design of the freezer heat exchanges leads to high approach temperatures between the refrigerant and the mix and, as a result, to lower efficiency.
Both inefficient designs of the condenser and the freezer lead to inherently low thermodynamic efficiency of the self-contained machines on the market.
The machines in self-service operations are usually installed in one row close to each other so the air inlet of one machine is facing the hot air outlet of the other. As a result, the cooling air temperature of the condenser may well exceed the environment temperature which causes further detrimental effect on the efficiency of the machine.
The machines are usually equipped with small compressors with inherently low isotropic efficiency. Moreover these compressors are driven by single phase permanent split-capacitor or PSC motors with inherently low efficiency (below approximately 60% in comparison to more than approximately 90% for three-phase motors).
One of the most expensive parts of a soft-serve machine is the stainless steel cabinet. The expensiveness of the cabinet may be explained by the high cost of the stainless steel as well as relatively small manufacturing batches which may not justify the use of highly expensive automated stamping machinery and tooling. Most parts of the cabinet are located behind the wall dividing the service and client areas and are not seen by clients. Getting rid of these enclosures may significantly reduce the manufacturing cost of the machines.
Most soft-serve machines utilized in self-service restaurants have three spigots: two spigots for the flavors produced by the machine and one for the mix of them. These spigots are located very close to each other so when a client uses a machine to dispense one flavor, the other spigots is not accessible for anyone else. As a result, the efficiency of the business in the period of high demand may be drastically reduced.
The control and monitoring panels of the machines are located on the client side. In case of any fault or warning message on the monitoring panel, the service personnel must at least temporarily restrict client access to this machine until the problem is resolved. In some operations, for example, resetting the safety relays requires access to the back as well as the front of the machine. The client doesn't need any information or control of the machine accept of operating the levers of the spigots, so location of the control and monitoring panel on the front of the machines is pointless.
The conventional soft service machines have two major types of hoppers: gravity and pump fed. Gravity fed hoppers are located above the freezers so the gravity may drive the liquid mix together with air from the hoppers into the freezers. High location of the hoppers creates considerable difficulty in loading and servicing the hoppers. To more efficiently utilize the very limited space inside the machines, the hoppers have a rectangular shape. The cooling of the mix is done by refrigeration coils wounded around the vertical walls of the hoppers. As a result, the cooling of the liquid is inhomogeneous. Temperature of the liquid in the central part of the hopper may exceed the safe limit while the liquid in the corners may be frozen. The other shortcoming of the gravity hoppers is inconsistency of overrun (the measure of the quantity of air in the product). The overrun strongly depends on the level of the liquid mix in the hopper. The overrun increases when the level drops causing detrimental effect on the quality of the product.
In the pump fed systems, the hoppers may be located close to the bottom of the machine in a specially refrigerated compartment. A pump draws the liquid from the hopper, mixes it with air and injects the foam into the freezer. Such systems allow keeping overrun considerably more stable, increasing the product quality. Also they are easier to refill and service. They are more expensive in comparison to the gravity fed systems. The other drawback of a pump fed system is difficulty of priming (initial filling the cylinder with mix foam). Most machines utilizing pump fed systems have a manual valve which must be open to allow the air out of the freezer until it is completely full with foam mix.
Sanitary regulations require regular cleaning the freezers and the hoppers of each machine. Each freezer, dispensing door, and hopper must be disassembled, cleaned using special, expensive solutions, washed, lubricated and assembled again. It is a very time consuming operation, requiring well-trained staff. The alternative to the cleaning may be pasteurization where all parts which may be in contact with the mix are subjected to heating to approximately 80° C. There are on the market machines which are capable of doing that by reversing the refrigeration cycle so the cooling coil in the freezer becomes the condenser and the compressor compresses the refrigerant gas to high pressure and temperature. Such machines tend to be much more expensive than conventional ones and are rarely utilized in self-service restaurants.
Therefore it would be desirable to have an apparatus specially designed for a self-service model of business operation, that doesn't have all the shortcomings of conventional machines and at the same time drastically reduces the cost of the business.